Revert "Include a system message that an agent was spawned (since the… #5110

Job	Run time
build-and-check	2m 27s
test-.agents	45s
test-npm-app	40s
test-common	46s
test-backend	49s
test-packages/agent-runtime	45s
test-cli	1m 8s
test-sdk	49s
test-web	54s
test-integration-packages/agent-runtime	38s
test-integration-npm-app	38s
test-integration-web	48s
test-integration-sdk	59s
test-integration-packages/internal	56s
test-packages/billing	46s
test-integration-backend	42s
test-integration-common	41s
test-integration-cli	46s
test-integration-packages/billing	40s
test-packages/internal	43s
test-integration-.agents	1m 18s
	18m 38s

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